A Straightforward Descriptor for the Deactivation of Zeolite Catalyst H-ZSM-5

Abstract

Catalyst deactivation during the methanol-to-hydrocarbons (MTH) reaction was investigated using five different commercially prepared microporous catalysts, including Mordenite, ZSM-22, ZSM-5, zeolite Beta and SAPO-34. The reaction was carried out in a fixed bed reactor at a constant feed rate per gram of catalyst. Deactivated and partially deactivated catalysts were obtained at increasing reaction times. The whole of the catalyst beds were characterized using nitrogen adsorption, thermogravimetric analysis, a dissolution-extraction protocol, and UV-Raman spectroscopy, focusing primarily on methods suitable for the quantification of the coke. The results illustrate that topology is the dominant parameter that influences not only catalyst lifetime and product distribution, but also the nature of the species causing the deactivation. For all catalyst topologies, when the entire catalyst bed is examined together, the micropore volume and BET surface area decrease more rapidly than total coke from TGA increases at short reaction times. In the materials with the more restricted access to the internal voids, such as ZSM-22 and SAPO-34, the loss of activity is to a large extent due to species which are soluble in dichloromethane and give rise to distinct features in the Raman spectra. For the Mordenite and Beta catalysts, which have larger pores comprising three dimensional networks, and to some extent for the ZSM-5 catalyst employed, the accumulation of more coke species which are insoluble in dichloromethane, presumably on the external surface of the zeolite crystals, is observed. This is linked to the appearance of more pronounced D and G bands in the Raman spectra, indicative of extended carbon species.

The Effect of Co-feeding Methyl Acetate on the H-ZSM5 Catalysed Methanol-to-Hydrocarbons Reaction

“…We attribute these differences to a greater degree of methylation of the aromatic rings in the presence of MeOAc. Highly methylated aromatics have been linked with ZSM-5 deactivation [19,25], which could explain why the increase in MeOAc has also nudged the catalyst in to a deactivation stage earlier than is seen with either methanol or DME. This enhanced extent of methylation in the adsorbed aromatic hydrocarbons appears to be the only significant difference in the INS spectra between the coke deposits formed in the presence and absence of MeOAc.…”

Deactivation of Zeolite Catalyst H-ZSM-5 during Conversion of Methanol to Gasoline: Operando Time- and Space-Resolved X-ray Diffraction

“…In a recent study of H-ZSM-5 relying on cumbersome ex situ methods, we were able to demonstrate that that the unit cell of the crystalline catalyst changes upon deactivation, at both atmospheric and elevated reaction pressure. We were able to establish a correlation between these changes and classical deactivation parameters, such as the total amount of coke, the remaining acidity, and the remaining surface area 16 . However, the extent to which these observations, made "post mortem" can be transferred to the working catalyst needs clarification.…”

Mesoporous H‐ZSM‐5 for the Conversion of Dimethyl Ether to Hydrocarbons

“…As the dehydration of methanol is taking place upstream to the gasoline synthesis step, the conversion of dimethyl ether (DME) to hydrocarbons is less exothermic. Furthermore, DME conversion enhances the carbon efficiency compared to methanol conversion . Since the 1970s H‐ZSM‐5 has been well investigated and established for this reaction because of the low coking tendency and an adequate product distribution , .…”